Babies as young as six months remember more than we thought

Robert Sciarrino/The Star-LedgerFifteen-month-old Joe Mulligan, with mother Debbie, participates in a study at the Cognitive Development Lab of Rutgers University. Research on even younger subjects find that babies remember and understand better than thought.

What do babies remember?

Adults can’t recall their own infant years, so they often assume babies themselves don’t remember much, either.

That assumption is wrong, as researchers at Rutgers University continue to prove. Their latest discovery, published in the journal Psychological Science, is that even when babies can’t remember the details of a missing object, they do remember it exists.

"It’s not easy to study babies and toddlers. They don’t cooperate," says Alan Leslie, director of the university’s Cognitive Development Lab on Busch Campus, Piscataway. Babies can’t talk, point, follow instructions or answer questions. Often they cry and squirm.

Yet babies and toddlers learn at a fabulous pace. From the end of the second year through the sixth, children expand their vocabularies by an average of eight to 10 words a day. "They are just the most amazing learning machines in the known world," says Leslie.

Even before they acquire words, they are already learning at a rate unsurpassed by any other stage of life. Unraveling the mysteries of this crucial pre-verbal stage could ultimately shed light on how and when humans learn. That in turn could offer insights into autism and other development disorders, Leslie said.

To determine how much an infant can remember, researchers at the lab devised a version of "two-card monte" for 6-month-olds. (Infants can keep track of three items; adults, just four.)

Earlier studies demonstrated that when a baby viewed an object subsequently hidden behind a screen, she wouldn’t notice if the screen was lifted to reveal a different object. It was assumed this meant the baby had simply forgotten the first object.

Leslie’s latest study shows it’s a bit more complicated.

This one focuses on shape, because infants learn about an object’s shape before any other of its traits. Parents often try to teach a baby about colors — with little success, Leslie said. "Color doesn’t tell you much about something," he said. "What would help you figure out something was a shoe — its shape, or its color?"

In the experiment, a baby watches as a triangle is placed behind a screen. Next the baby watches as a second object — a disk — is placed behind a second screen.

Then the first screen is removed to reveal one of three scenarios: the original triangle, the disk (switched from behind the other screen), or nothing at all.

The baby’s reaction is observed, with researchers filming the baby’s head and shoulders.

If the baby stares at the revealed space for just two seconds or so, it means she has seen what she expected to see. But if she stares longer — 12 to 15 seconds — it indicates puzzlement, as she tries to acquire more information to make sense of what she has seen.

In cases when the objects were switched, babies showed little reaction to seeing a different shape. They apparently retained no memory of the first object’s shape, so conveyed no confusion when presented with a different shape. The object’s shape had simply dropped out of the immature brain’s memory.

But when the object disappeared — if the screen lifted to reveal emptiness — the babies showed great surprise. Although they couldn’t remember what they expected to see, clearly they expected to see something.

In short, they retain an inkling of the object, Leslie found. This means the very notion of physical existence is understood at a younger age than previously thought.

The study’s co-author is Melissa Kibbe, of Johns Hopkins University, a formerly doctoral student at the Rutgers lab.

Although the lab doesn’t specialize in studying autism, its work in establishing a more precise timeline of infancy’s mental and emotional milestones may help shed light on that condition.

For example, Leslie’s earlier research examined how much babies understand about what other people experience.

In that experiment, a baby sits in front of a little puppet theater, watching as a puppet hides a colorful ball in one covered box, then switches it to a second covered box. These actions are viewed as well by a woman standing behind the theater, who reaches down to open the correct box each time.

Then the woman is distracted by the sound of a telephone, and looks away. At that moment, the puppet switches the ball from Box A to Box B. Her attention then returns to the scene. Having missed the switch to Box B, in which box will the woman look?

Infants know the answer to that, it turns out. When researchers track their eye movements, they find most babies will look at Box A — the one in which the woman would expect to find the ball. Even as infants, they realize the woman doesn’t know what they know; she didn’t see the switch that took place when she was distracted.

Yet autistic children as old as 7 or 8 don’t appear to grasp this, said Leslie. They saw the ball switched to Box B and can’t understand the woman doesn’t realize that. When autistic children are older, they are said to be unable to put themselves in someone else’s shoes. Infant research demonstrates that in normal development, this core ability arrives very early in life.

In fact, researchers continue to be surprised by just how much babies know, Leslie said, as time and again the babies prove assumptions wrong. "We keep underestimating them," he said.